This invention relates to a clutch/brake unit and more particularly to a wrap spring clutch/brake unit of the type in which the clutching and braking action is produced in response to the contraction of helical springs.
A clutch/brake unit of this general type is disclosed in Brunelle U.S. Pat. No. 3,559,781. Such a unit includes relatively rotatable input and output hubs which are encircled by a helical spring. When contracted, the spring couples the two hubs together for rotation in unison and, when expanded, allows the input hub to rotate relative to the output hub.
A second helical spring encircles the output hub and a rotationally fixed brake hub. When the brake spring is contracted, it couples the output hub to the brake hub in order to prevent rotation of the output hub. Upon expansion of the brake spring, the output hub is released to rotate with the input hub and to rotate relative to the brake hub. The brake spring is expanded and contracted when the clutch spring is contracted and expanded, respectively.
Expansion and contraction of the springs is effected by a control collar. One tang of each spring is connected to the control collar while the second tang of each spring is connected to the output hub. The clutch spring normally is contracted around both the input hub and the output hub and normally causes the control collar to rotate in unison with those hubs. When rotation of the collar is stopped, the collar causes the clutch spring to expand and causes the brake spring to contract.
It is necessary to locate the tangs of the clutch and brake springs in precise angular positions relative to one another in order to establish a proper torsional differential between the two springs. In the clutch/brake unit of the Brunelle patent, this is achieved by forming multiple angularly spaced notches around each end of the control collar and by placing the tang of each spring in a selected notch. While this arrangement enables fine and precise adjustment of the spring differential, the adjustment can be effected only by removing the tangs from the selected notches and placing the tangs in different notches. This requires that several components of the clutch/brake unit be completely disassembled and then reassembled.